1. Field of the Invention
The present invention relates to a rotary vane compressor for an air conditioning system used in a vehicle such as an automobile, and more particularly, relates to a variable displacement vane compressor which comprises a cylinder assembly including a cylindrical body having a bore and opposed end wall members secured to the opposed ends of the cylindrical body, respectively, for closing open ends of the bore, and a rotor disposed within the bore for rotation so as to form at least one crescent chamber between the rotor and the bore of the cylinder assembly for receiving a refrigerant, the rotor having at least one vane which is extendably fitted in the rotor so that the free end of the vane is in contact with the circumferential inner wall surface of the bore during the rotation of the rotor, whereby when the vane passes through the crescent chamber, the refrigerant is capable of being compressed, wherein an amount of the refrigerant which is introduced into the crescent chamber is adjustable in response to a change of a cooling load at the air conditioning system.
2. Description of the Related Art
Conventionally, a variable displacement vane compressor used in an air conditioning system for a vehicle such as an automobile is driven by the motor of the automobile, and the room temperature of the automobile is adjustable to a temperature at which a driver and passengers feel comfortable under ambient conditions. When a cooling load which the air conditioning system must bear becomes very high, the compressor must be run at the maximum cooling capacity thereof, whereas when the cooling load becomes lower, the compressor must be run at a lower cooling capacity. When the room temperature once reaches a comfortable temperature, preferably the compressor is run at the low cooling capacity at which the comfortable temperature can be maintained.
Japanese Unexamined Patent Publication No 59-99089, filed by the same applicant, discloses a variable displacement vane compressor wherein an amount of the refrigerant, which is introduced into the crescent chamber, is adjustable in response to a pressure change of the refrigerant returned from the evaporator of the air conditioning system to the compressor. Particularly, the compressor is constructed so that an opening area for introducing the refrigerant from a suction chamber of the compressor, which is connected to the evaporator of the air conditioning system, into the crescent chamber can be throttled in response to a pressure change of the refrigerant within the suction chamber. When the air conditioning system is under a high cooling load, a large amount of the refrigerant is evaporated in the evaporator and the pressure of the refrigerant is increased within the suction chamber. Accordingly, in the compressor, as the pressure of the refrigerant is further increased in the suction chamber, the opening area is made larger so that a larger amount of the refrigerant is introduced from the suction chamber into the crescent or compressing chamber, whereby the compressor can be run at a higher cooling capacity. Conversely, when the air conditioning system is under a low cooling load, the refrigerant pressure of the suction chamber is further lowered. In this case, the throttling of the opening area for introducing the refrigerant from the suction chamber into the compressing chamber is increased so that a smaller amount of the refrigerant is introduced from the suction chamber into the compressing chamber, whereby the compressor is run at a lower cooling capacity.
This conventional compressor can be run efficiently at a high operation speed, because the best throttling effect of the opening area can be obtained only at such a high operation speed. Namely, at a low speed operation, it is impossible to obtain the optimum throttling effect of the opening area. This is because, although the opening area is throttled and made small, a relatively large amount of the refrigerant may be introduced from the suction chamber into the compressing chamber due to the low speed operation, and thus the compressor cannot operate at optimum efficiency at the low cooling capacity during a low speed operation. The running or operation speed of the compressor depends upon the engine speed of an automobile, and when the automobile is driven at a low speed, the compressor must run at a low operation speed. Accordingly, if the compressor is required to be run at a low cooling capacity, it is impossible to meet this requirement for the reasons mentioned above.
The same inventors have proposed a variable displacement vane compressor wherein a compression stroke carried out by the vane is adjustable in response to a pressure change of the refrigerant within the suction chamber of the compressor, whereby an amount of the compressed refrigerant discharged from the compressor into the air conditioning system can be varied in response to a change of a cooling load at the air conditioning system. Particularly, this compressor includes an annular plate member rotatably disposed between one of the end wall members of the cylinder assembly and the cylindrical body thereof. The annular plate member has an actuator slot formed therein which is extended in a direction of rotation of the vane and which opens into the crescent or compressing chamber. The vane passes through the crescent chamber in such a manner that it divides the crescent chamber into a front section and rear section, with a volume of the front section being gradually decreased while a volume of the rear section is gradually increased. While the vane advances along the arcuate slot of the annular plate member, a part of the refrigerant received in the front section is allowed to escape into the rear section through the arcuate slot, and thus a compression stroke carried out by the vane starts just after the vane have passed through the arcuate slot of the annular plate member. With this arrangement, it is possible to adjust the compression stroke by moving the annular plate member having the arcuate slot in a direction of rotation of the vane; the movement of the annular plate member being carried out in response to a pressure change of the refrigerant within the suction chamber of the compressor.
This vane compressor can be run at optimum efficiency only when a speed of operation thereof, which depends upon the engine speed of the automobile, is low. This is because, when the speed of operation is high, a part of the refrigerant received in the front crescent chamber section cannot properly escape into the rear crescent chamber section through the arcuate slot of the annular plate member, due to the inertia of the refrigerant gas.